In an image forming apparatus such as a laser printer, an electrostatic latent image is formed on a surface of a photosensitive drum, and toner is fed to the elastic latent image from a developing device, whereby a toner image is formed on the surface of the photosensitive drum. Then, the toner image is transferred to a sheet of paper, and the image is formed on the sheet.
The developing device includes: a housing having an opening which is open towards the photosensitive drum; and a developing roller which is supported rotatably in the opening of the housing. Toner is held within the housing. The developing roller is configured such that a roller main body formed of a conductive elastic material is provided on and covers a metallic roller shaft. In the developing roller, a portion of a circumferential surface of the roller main body is exposed from the housing, and the exposed portion faces a surface of the photosensitive roller. The toner in the housing is carried on the surface of the roller main body of the developing roller, and the toner so carried is then fed to the surface of the photosensitive roller in association with the rotation of the developing roller, and the toner is fed to the electrostatic latent image that is formed on the surface of the photosensitive drum.
In the developing device, side seals are provided for preventing the leakage of the toner from both sides of the roller main body. Each side seal is formed by affixing a sliding frictional member formed of fibers to a sponge member made from urethane foam. The side seals are respectively secured to positions which face both end portions of the roller main body of the developing roller. When the developing roller is attached to the housing, the sliding frictional members are brought into contact with portions of the circumferential surface of the roller main body which extends inwards from both edges of the circumferential surface by a predetermined width, whereby the side seals are pressed by the developing roller. The sponge member has an appropriate thickness, and when the developing roller is attached to the housing, the sponge member is compressed between the roller main body and the housing so as to produce an appropriate elastic force. By this elastic force, the side seals (the sliding frictional seal members) are brought into press contact with both the axial end portions of the roller main body, whereby seals are established between both the end portions of the roller main body and the housing by the side seals. This kind of the developing device is disclosed in JP-2003-A-195630, for example.